samples/array_mapreduce.js

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// Usage: jjs array_mapreduce.js

// Many Array.prototype functions such as map,
// filter, reduce, reduceRight, every, some are generic.
// These functions accept ECMAScript array as well as
// many array-like objects including java arrays.
// So, you can do map/filter/reduce with Java streams or
// you can also use Array.prototype functions as below.
// See also http://en.wikipedia.org/wiki/MapReduce

var DoubleArray = Java.type("double[]");
var StringArray = Java.type("java.lang.String[]");

var map = Array.prototype.map;
var filter = Array.prototype.filter;
var reduce = Array.prototype.reduce;

var jarr = new StringArray(5);
jarr[0] = "nashorn";
jarr[1] = "ecmascript";
jarr[2] = "javascript";
jarr[3] = "js";
jarr[4] = "scheme";

// sum of word lengths
print("Sum word length:",
    reduce.call(
        map.call(jarr, function(x) x.length),
        function(x, y) x + y)
);

// another array example involving numbers
jarr = new DoubleArray(10);
// make random array of numbers
for (var i = 0; i < jarr.length; i++)
    jarr[i] = Math.random();

var forEach = Array.prototype.forEach;
// print numbers in the array
forEach.call(jarr, function(x) print(x));

// print sum of squares of the random numbers
print("Square sum:",
    reduce.call(
        map.call(jarr, function(x) x*x),
        function(x, y) x + y)
);